Please help me out. 1969 100w build

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Tazin
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Re: Please help me out. 1969 100w build

Post by Tazin » Fri Jun 08, 2018 3:14 pm

If there is something wrong other than a bad solder joint, I'd say it's either at the 120Vac input connection or possibly something with the ON/OFF switch. Also double check the Mains Fuse holder and its connections.

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Sun Jun 10, 2018 8:33 pm

I went through all solder joints with regard to the power supply and now have everything in good shape except for V3, showing high voltages.

Here's a link to see the chart: https://www.flickr.com/gp/wedinbordeaux/5yj772

What's next?

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Mon Jun 11, 2018 3:58 pm

I do not think you are wired correctly.

The orange and green wires should go to the lugs with the 220k resistors on them (i.e. under your stand off). These are the grid leak resistors and must be hooked up to bias the output tubes.

The pots effectively go between the coupling caps on the stand-off with the pair of wires to the pots and then the return wires from the pots go to the bottom lugs, look here:

http://valvestorm.com/sites/default/fil ... 20Step.pdf
Neil

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Mon Jun 11, 2018 9:39 pm

I fixed wiring - voltages on that tube remain the same. photos: https://www.flickr.com/gp/wedinbordeaux/S57j97

Tazin
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Re: Please help me out. 1969 100w build

Post by Tazin » Mon Jun 11, 2018 10:57 pm

Did you try swapping preamp tubes to eliminate a possible bad tube in the V3 slot?

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Mon Jun 11, 2018 11:04 pm

yes, I moved all (3) 12ax7 tubes within the 3 sockets and get the same readings.

Tazin
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Re: Please help me out. 1969 100w build

Post by Tazin » Tue Jun 12, 2018 12:37 pm

You could check for dc voltage on the Purple (violet) wire at the middle solder lug of the Treble pot. You could also check the voltage at the 1/2w 10K resistor (the resistor linked to the two 1 Meg & 470-ohm resistors)...I would check the voltage at the end where the black sleeved jumper wire connects to the 1/2w 10K resistor.
Are all the resistors in that area for V3 (two 1 Meg, 470-ohm, 10K) within specs?

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Tue Jun 12, 2018 2:13 pm

0V on the center lug of the treble pot. Voltage at 1/2W 10K is 102V. I removed 1 side of each of the 3 resistors stated and they all check within specs.

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Re: Please help me out. 1969 100w build

Post by Tazin » Tue Jun 12, 2018 2:46 pm

Hum...What's weird is that the ratios between the voltages for V3 is about right but their all just high.
All the solder connections at the V3 socket look good?...No stray wire strands accidentally touching one another?
Does the voltages on V3 change if you remove that preamp tube but leave just the first two preamp tubes in?

Kinda thinking out loud here...I don't think it would be something with the H.T. rail since all the other voltages on the rail are appearently correct...And the odds of both V3 plate resistors (the 100K & 82K) being bad are very slim at best. So, the extra voltage has to be (or could be) coming from either a short somewhere or possibly from the negative feedback wire. What if you disconnect the NFB wire at the Speaker jack or the Selector; tape it off so it doesn't short against anything, then reinstall all three preamp tubes (no output tubes) and take a voltage reading at V3?

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Tue Jun 12, 2018 3:14 pm

connections at the V3 socket look good
removing V3 gives these voltages:
1 2 3 4 5 6 7 8 9
388 0 0 3.45 3.45 389 0 0 3.45

disconnect NFB wire at the impedance selector, three preamp tubes installed (no output tubes) V3:

1 2 3 4 5 6 7 8 9
390 325 364 3.45 3.45 389 326 366 3.45

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neikeel
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Re: Please help me out. 1969 100w build

Post by neikeel » Tue Jun 12, 2018 3:38 pm

Where is your presence pot grounded?
Neil

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Tue Jun 12, 2018 4:25 pm

Presence pot is grounded to the F6 cap ground lug.

Since voltages changed when I added the master volume control, do you think it is possible I damaged a component when I connected the bias wires incorrectly?

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Re: Please help me out. 1969 100w build

Post by Tazin » Tue Jun 12, 2018 5:20 pm

Just for shits-n-giggles I decided to check one of my amps...
With V3 installed (no output tubes; 524Vdc at Pin# V5):
-1---2----3---4-----5----6----7----8---9 (Pin#'s)
229 25--40---H----H---222--26--40--H (Voltages Vdc)

Without V3 installed:
-1----2---3---4----5-----6---7---8---9 (Pin#'s)
359 -0---0---H----H---354--0---0---H (Voltages Vdc)

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Re: Please help me out. 1969 100w build

Post by no0sand1s » Tue Jun 12, 2018 5:25 pm

and did you giggle?

Tazin
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Re: Please help me out. 1969 100w build

Post by Tazin » Tue Jun 12, 2018 5:29 pm

no0sand1s wrote:
Tue Jun 12, 2018 4:25 pm
Presence pot is grounded to the F6 cap ground lug.

Since voltages changed when I added the master volume control, do you think it is possible I damaged a component when I connected the bias wires incorrectly?
Anything is possible but it seems unlikely since all the components in that area are rated to handle the "normal" working voltages and beyond. There doesn't seem to be any damaged components in the tail section of the PI since you already checked those resistors. You could the PI plate resistors (the 100K & 82K) just to make sure they haven't gone out of spec.

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